1. Field of the Invention
The present invention relates to a lens driving apparatus used in an optical instrument such as a camera.
2. Related Background Art
A conventionally known lens driving apparatus in an optical instrument such as a camera comprises a plurality of lens barrels which telescopically expand from a camera body, and front and rear lens groups arranged therein, in which the front and rear lens groups are appropriately moved along the optical axis as the lens barrels expand or collapse, changing magnification and adjusting focus. For example, a lens driving apparatus in which a cam ring rotating about the optical axis holds front and rear lens groups by way of respective cam grooves different from each other and rotates so as to move the front lens group and rear lens group according to the forms of cam grooves has been disclosed in Japanese Patent Application Laid-Open No. HEI 9-49958.
In this lens driving apparatus, the cam groove for the rear lens group has a width greater than that of the cam follower of the rear lens group, so that the rear lens group moves in conformity to the cam groove when the cam ring rotates normally, whereas the width of cam groove prevents the rear lens group from moving when the cam ring rotates in reverse, so as to adjust the focus as appropriate.
In the lens driving apparatus disclosed in the above-mentioned publication, however, there is a fear of the rear lens group moving at the time of focus adjustment without being sufficiently held. Therefore, if an external force such as shock acts thereon, then the position of rear lens group may shift, whereby the focus adjustment may not be carried out appropriately.
For overcoming such a problem, there has been proposed, as disclosed in Japanese Patent Application Laid-Open No. HEI 11-64708, a lens barrel for expanding an intermediate barrel and a movable barrel from a camera body, in which a cam barrel moving together with the intermediate barrel is disposed inside the intermediate barrel. In this lens barrel, the front lens group is held by the movable barrel, the rear lens group is held by the cam barrel by way of a cam groove, and a special gear is provided for transmitting a rotational force from the intermediate barrel to the cam barrel at the time of normal rotation without transmitting the rotational force at the time of reverse rotation. Therefore, the rear lens group can sufficiently be held by way of the cam barrel and cam groove even at the time of focus adjustment due to the gear in mesh.
However, this lens barrel is problematic in that the lens driving apparatus increases its size and cost since it necessitates the cam barrel and rotation transmitting mechanism as components constituting its lens driving mechanism.
In order to overcome such problems, it is an object of the present invention to provide a lens driving apparatus which can carry out appropriate focus adjustment, and can be made smaller at a lower cost.
For achieving such an object, in a first aspect, the present invention provides a lens driving apparatus for moving at least two lens groups composed of first and second lenses along an optical axis so as to change a magnification and adjust a focus, the lens driving apparatus comprising a first barrel, disposed so as to be expandable and collapsible in an optical axis direction, for moving the first lens in the optical axis direction along with expanding and collapsing thereof; a second barrel, disposed concentric with the first barrel while being expandable and collapsible with respect to the first barrel along with the expanding and collapsing of first barrel, for moving the second lens in the optical axis direction when expanding from the first barrel; and holding means for holding the second lens when the second barrel is switched from expanding to collapsing, so as to move the second lens together with the first barrel.
In a second aspect, the present invention provides a lens driving apparatus for moving at least two lens groups composed of first and second lenses along an optical axis so as to change a magnification and adjust a focus, the lens driving apparatus comprising a first barrel, disposed so as to be expandable and collapsible in an optical axis direction, for moving the first lens in the optical axis direction along with expanding and collapsing thereof; a second barrel, disposed concentric with the first barrel while being expandable and collapsible with respect to the first barrel along with the expanding and collapsing of first barrel, for moving the second lens in the optical axis direction when collapsing into the first barrel; and holding means for holding the second lens when the second barrel is switched from collapsing to expanding, so as to move the second lens together with the first barrel.
In a third aspect, the present invention provides a lens driving apparatus for moving at least two lens groups composed of first and second lenses along an optical axis so as to change a magnification and adjust a focus, the lens driving apparatus comprising a first barrel, disposed so as to be expandable and collapsible in an optical axis direction, for moving the first lens in the optical axis direction along with expanding thereof; a second barrel, disposed concentric with the first barrel while being expandable and collapsible with respect to the first barrel along with the expanding and collapsing of first barrel, for moving the second lens in the optical axis direction when expanding and collapsing with respect to the first barrel; and holding means for holding the first lens when the first barrel is switched from expanding to collapsing, so as to move the first lens together with the first barrel.
In a fourth aspect, the present invention provides a lens driving apparatus for moving at least two lens groups composed of first and second lenses along an optical axis so as to change a magnification and adjust a focus, the lens driving apparatus comprising a first barrel, disposed so as to be expandable and collapsible in an optical axis direction, for moving the first lens in the optical axis direction along with collapsing thereof; a second barrel, disposed concentric with the first barrel while being expandable and collapsible with respect to the first barrel along with the expanding and collapsing of first barrel, for moving the second lens in the optical axis direction when expanding and collapsing with respect to the first barrel; and holding means for holding the first lens when the first barrel is switched from collapsing to expanding, so as to move the first lens together with the first barrel.
In the lens driving apparatus in accordance with the present invention, the holding means may comprise an engaging member having a spherical part, and urging means for pressing the spherical part of the engaging member against a movable member moving together with the first barrel, so as to hold the first or second lens by causing the spherical part to engage a groove formed in the movable member.
In the lens driving apparatus in accordance with the present invention, the movable member may be a straight member attached to the first barrel and adapted to move in the optical axis direction together with the first barrel.
Since the present invention comprises holding means for holding the first or second lens so as to move it together with the first barrel when the movement of the first or second barrel is reversed, the distance between the first and second lenses can be changed between the expanding and collapsing of the first and second barrels, whereby the focus can be adjusted. If this holding means is configured so as to accompany an existing component, then the number of components employed for changing the magnification and adjusting the focus can be reduced, whereby the apparatus as a whole can be made smaller at a lower cost.